2.7-dihydroxynaphthalene-3.6-dicarboxylic acid



Patented Feb. 7, 1931;

UNITED STATES PATENT creme HEINRICH monscnnn, 0F oonoenn nnnrannnWILHELM LUCE, or northern-on- THE-TAUNUS, GERMANY, ASSIGNOR-S T0 GENERALANILINEW'QBIKS, INC 'OFQNEWJ YORK, N. Y., A CORPORATION OF DELAWARE V I2.7-DIHYJJR0XYNAPirrnnrnnnaemmnnnoxymo ACID" No Drawing. Applicationfiled January 5, 1932, Serial No, 584,888,3am1in Germany-January 12,1931.

The present invention relates to a new hydroxynaphthalene-carboxylicV,acid, more particularly it relates to the2.7-dihydroxynaphthalene-3.6-dicarboxylic, acid which may be representedby the following formula:

HO OH nooo -ooon Our new hydroxynaphthalene-carboxylic acid isobtainable by reacting with carbondioxide under superatmosphericpressure upon the alkali metal salts of 2.7-dihydroxynaphthalene at atemperature of at least 250 (1, say at temperatures between 250 and 350.C. Otherwise the '2.7dihydroxynaphthalene-3.6-dicarboxylic acid isobtainable by causing carbon-dioxide to act under super-V acid, whichhas been described in literature.

(compare Ber. d. Deutschen Chem. Gesellschaft, vol. 26, 1893, page1117).

The free acid is isolated in the usual man- I ner by dissolving thereaction mass in water and acidifying the solution, for example with amineral acid.

From unchanged 2.7-dihydroxynaphthalene-3-carboxylic acid or from somemonocarboxylic acid formed in the reaction, the 3.6-dicarboxylic acidcan be easily separated due to its property of being more dificultlysoluble in water than the monocarboxylic acid, said process of workingup the reaction mass being more fully described in the examples.

The new 2.7 -dihydroXynaphthalene-3.6- dicarboxylic acid is a yellowishsubstance, decomposing at temperatures above 300 C., dificnltly solublein water, more easily soluble in aqueous alkalies and is a valuableinter- H16%lt1t product in the manufacture of dyestu s.

H ,Theinventionis illustratedby the following' examples, but is notlimited thereto! a 1,.

E wq-mple J.-.The dipot a'ssium' salt 0f 2,75 dihydroxynaphthalene isheated for 10 hours.

at28O Gland under .a carbon-dioxide pre's- The reaction'prodsure of 40atmospheres.- uct is allowed-to cool, is; dissolved in a large quantityof hotfwate'rf and filtered from impurities. on acidifying the hotfiltrate the 2.7dihydroxynaphthalene 3.6 dicarboxylic acid isprecipitated. From the mother liquor there separate on cooling the moreeasily soluble 2.7-dihydroxynaphthalene-3-carboxylic acid and someunchanged 2.7-dihydroxynaphthalene. With pyridine freefrom water, the

27 dihydroxynaphthalene 3.6.- dicarboxylic aci'd forms a dificultlysoluble pyridiniumj salt. The free acid dissolves in aqueous causticalkalies and inaqueous alkali metal carbonates with a yellowish-browncoloration. Its alkali metal salts are less soluble than those of themonocarboxylicacid salts and can be separated rather quantitatively fromthe aqueous solutions by the addition of common salt.

' Example 2.-A mixture of 1 part by weight of 2.7-dihydroxynaphthaleneand 3 partsby Weight of potassiumcarbonate is heated for 16 hours at 340C. under a carbon-dioxide pressure of 80 atmospheres. After coolso ingthe reaction product is dissolved in hot water and filtered from.impurities. On acidifying the filtrate, the2.7-dihydroxynaphthalene-3.G-discarboxylic acid is ,pre cipitated.

Example 3.-The tripotassium salt of 2.7-

dihydroxynaphthalene-3-carboxylic acid is heated for 15 hours at 280 C.under a carbondioxide pressure of 50 atmospheres. The reaction productis worked up as described in Example 1. Example 4.One molecularproportion of 2.7-dihydroxynaphthalene is dissolved in two molecularproportions of aqueous caustic soda lye. The solution is evaporated todrynessand the disodium salt thus obtained is carefully freed fromwater. The saltfree from water is treated with carbon-dioxide at atemperature of 230 C.', while stirring.

When the carbon-dioxide; pressure has 99 reached 45 atmospheres, thetemperature is raised to 300 C. and kept at this temperature for 4hours, while stirring and maintaining a carbon-dioxide pressure of, 45at- 5 mospheres. The peaction product; is worked up as described inExample 1.

We claim: 1. As a new product the 2.7d-i'hydroxynaphthalene-3.6-dicarb0xy1ie acid of the fol- 1o lowingformula:

HO OH being a yellowish substance, difiicultly s0l able in water, moreeasily soluble in aqueous alkalies and being a valuable intermediateproduct in the manufacture of dyestufls.

In testimony whereof,we afiix our signatures.

HEINRICH MORSCHEL. WI HELMLUOE.

